Ui Ando was about 10 years old when the negative comments began. “People told me that I wasn’t normal,” says Ando, 22, who grew up near the city of Gifu in central Japan. “They said I was too heavy for a girl.” At school she was called debu or “fatty”. At university her classmates thought her rounder physique lent her a homely air. They nicknamed her “Mama”.

Today, at 5ft 3in tall and just over 11 stone (70kg), Ando is, coincidentally, exactly the same height and weight as the average British woman. But in Japan, a country that has the slimmest population in the developed world, she’s not so typical. Japanese women across all ages weigh an average of around eight-and-a-half stone. Fewer than 20% are officially overweight and a mere 3.2% are classified as obese. Combine this with a youth culture filled with childishly cute pop idols and petite fashion – the credo of kawaii – and it’s easy to see how larger women feel stigmatised. “For a long time I was very ashamed about my size,” says Ando.

Now Ando is at the forefront of a trend aimed at helping young women reject fat-shaming stereotypes. She is a model for La Farfa, Japan’s first fashion magazine for plus-size women. She is also one of a trio of singers in a new band, La Big 3, which is sponsored by the magazine. The group released its first single last month, a song entitled Pochative, roughly meaning “chubby-positive”. The pocchari (chubby) trend has also seen the emergence of another all-girl band, Chubbiness, whose members are slightly less svelte than regular idols, and a number of trendy clothing brands designed for more ample bodies.

It’s not a total departure from dominant beauty ideals though. Far from eschewing mainstream cuteness and the female infantilisation that goes with it, most young women like Ando want to be seen as desirably cute, too – only bigger-sized. They are embracing names such as “marshmallow girls”, “squishy girls” and “pudgy girls”, and adapting the frills and bows of kawaii street fashion to their own body shapes. Ando says the point is to have fun and show that “confidence and beauty have nothing to do with size”.

The pocchari trend came to the fore in March last year with the launch of La Farfa (the name is an abbreviation of “butterfly” in Italian). Publisher and editor-in-chief Harumi Kon says she started the magazine because she couldn’t find styles to suit her own larger figure. “Most clothes were too small, and the large clothes were always in boring dark colours or designed to hide your body,” she says. “I wanted to showcase bright, energetic fashions to make plus-size women shine.”

Kon teamed up with popular “chubby” comedian Naomi Watanabe, who had become famous a few years earlier when she performed an outrageous lip-synching impersonation of Beyoncé. (As in most countries, making people laugh is one area where fat women in Japan can find approval.) Watanabe appeared on the cover of the first issue, which sold out its print run of 50,000 copies, and she has been La Farfa’s cover girl ever since. “We now sell 100,000 copies per issue and have changed from publishing the magazine twice a year to publishing it bi-monthly,” says Kon.

Kon believes La Farfa’s success is due to its unflinching acceptance of real women’s bodies. For a start, most of the models are amateurs she found through auditioning ordinary women – there simply weren’t enough professional plus-size models. “Also, we never give advice about how to look slimmer and we don’t photoshop away rolls of fat, even after swimwear shoots,” says Kon. The magazine uses animal shapes to help women choose clothes for their body type – pigeon (big chested), penguin (big bottom half) and teddy bear (round in the middle). “The aim is to help women look pretty and fashionable the way they are, not to give them impossible ideals.”

The magazine’s platform also helped Watanabe launch her own plus-size clothing line last April. Punyus (onomatopeia for squishy) has a flagship store in the Shibuya 109 building, Tokyo’s legendary teen fashion hub, selling items such as denim pencil skirts, hats and bags imprinted with fruit and animals, and cable knits in pastel colours. Turning the tables in a beautifully clever way, the shop boasts that it sells some of its most fashionable styles in smaller sizes “so that thin women don’t miss out”.

Not everyone in Japan welcomes the pocchari trend. Some critics argue it’s just another way for the fashion industry to exploit women. Others complain that it could enable unhealthy lifestyles and encourage obesity. But Kimie Nakaguchi, 34, a GP in Tokyo, believes the trend is long overdue: 10 years ago, she almost died from using diet pills and other extreme methods to lose weight. (She says she was “husband-hunting” at the time). She is currently writing a book about her experience and the pressures on Japanese women to remain thin. “In general, the fashion for super-skinniness is far more dangerous to health than being a little overweight,” she says. “Many Japanese women actually eat too little.”

Whether that’s true or not, Japan’s low obesity rate doesn’t look set to change. Figures from the health ministry show that, in stark contrast to global patterns, body mass index (BMI) in Japan has been falling steadily for the past 30 years – people have been getting thinner. The government is also vigilant about preventing unhealthy weight gain. In 2008 it introduced a law stipulating maximum waist sizes for company employees over the age of 40; those who exceed the limits of 33.5in (86cm) for men and 35.4in (90cm) for women must undergo mandatory nutrition and exercise counselling.

Nakaguchi says she laughed out loud when she saw the video for La Big 3’s single featuring Ando and her bandmates in bright 1950s-style dresses using ice-cream cones as microphones, and tucking into fried chicken thighs with abandon. “Obviously it’s not good to eat too much junk food, but I don’t think the pocchari trend is advocating that. It’s telling women that they don’t need to hide their appetites. It’s telling them to please themselves rather than others,” she says. “These are messages that many Japanese women, including me, have waited a long time to hear.”